Telephone loops which are associated with a central office (CO) telephone facility are usually terminated at the CO by a line circuit. The line circuit is typically required to provide a terminating impedance of about 900 ohms for voice frequency signals on the loop. The line circuit is also required to supply energizing direct current for operation of the loop. However the source impedance of the energizing direct current is usually required to be about 400 ohms. This is typically arranged for by two similar resistors of about 200 ohms, each being connected in series with one of the tip and ring leads of the loop and a CO battery of about 50 volts. The line circuit usually must meet stringent requirements as to permissible levels of unbalance to ground, for example less than -60 decibels, and tolerance of longitudinal induction of up to 20 milliamperes rms per lead. The line circuit must also be able to survive high voltage surges of at least 500 volts without damage to itself or apparatus in the CO. All of these requirements are well satisfied by many prior line interface circuits. However, many attempts have been made to design line circuits of lesser cost through reducing the bulk of various circuit components and by utilizing newer devices including semiconductor components to replace the transformer. Many of these attempts involve penalties such as requirements for battery voltage boosters, or failure to meet all of the typical line interface circuit operational requirements, or are not yet cost competitive with present widely used line interface circuits.